Klinefelter Syndrome - Topic Overview

What is Klinefelter syndrome?

Klinefelter syndrome
is a
genetic disorder that affects males. Klinefelter
syndrome occurs when a boy is born with one or more extra X
chromosomes. Most males have one Y and one X
chromosome. Having extra X chromosomes can cause a male to have some physical
traits unusual for males.

Many men with an extra X chromosome are
not aware that they have it, and they lead normal lives. Males who have Klinefelter
syndrome may be described as X-Y males or males with X-Y syndrome. Klinefelter
syndrome occurs in about 1 out of 1,000 males.

What causes Klinefelter syndrome?

The presence of
an extra X chromosome in males most often occurs when the genetic material in the egg splits unevenly. But it can also occur when the genetic material in the
sperm splits unevenly. Even though Klinefelter syndrome is a genetic disorder, it is not passed down through families. So, parents who have a child with Klinefelter syndrome are not any more likely than other couples to have another child with the condition.

What are the symptoms?

Many men who have Klinefelter
syndrome do not have obvious symptoms. Others have sparse body hair, enlarged
breasts, and wide hips. In almost all men the testicles remain small. In some
men the penis does not reach adult size. Their voices may not be as deep. They
usually cannot father children. But they can have a normal sex life.

Some boys with Klinefelter syndrome have language and learning
problems.